By the term pyelonephritis is meant a combined inflammation of pelvis and kidney. As this inflammation is mostly septic the usual result is a suppurative nephritis. The disease mostly connects itself with that just described as suppurative inflammation of the pelvis and leads to a suppurative inflammation of the kidney.

There are two modes in which the condition may be brought about. On the one hand the irritating chemical products from the pelvis may be carried into the kidney, being absorbed either by the tubules or the lymphatics, or on the other hand the microbes may themselves propagate into the kidney. This latter method is much the more frequent. Colonies of micrococci have been observed in the uriniferous tubules as well as in the lymphatics.

The lymphatics of the kidneys, according to Steven and Newman, are in communication with those of the ureter. When an injection is thrown with some force into the ureter, it passes into the adventitia of this canal, and thence to the capsule of the kidney. The lymphatics of the capsule communicate with those of the kidney, so that stellate vessels are visible, in these injections, on the surface of the kidney, and are found to penetrate deeply into the cortex.

Pyelonephritis mostly manifests itself in the form of multiple abscesses in the kidneys, the extension being by the second method mentioned above. That is to say, micrococci propagate into the kidney in an irregular fashion and each colony of microbes becomes the focus of an abscess. The abscesses exist both in pyramids and cortex. They are scattered over the kidney so that the appearances may resemble those of pyaemia, but they are frequently in groups, occupying certain areas with a number of purulent centres. They are small in size but by coalescence may reach larger dimensions. The groups are frequently more or less wedge-shaped, the base at the cortex and the apex far down in the pyramid or even at its apex.

When the propagation is by the lymphatics the abscesses will bo chiefly on the surface of the kidney, partly involving the capsule. It is not uncommon to open abscesses in the process of stripping the capsule. It may happen that abscesses form by this mode of extension without the pelvis being affected, the propagation occurring by the wall of the ureter to the surface of the kidney, but generally both modes of extension co-exist, and there are abscesses in the substance as well as at the surface of the organ.

A more rare circumstance is that the entire organ is infiltrated, especially in the cortex, with leucocytes, and the appearances presented are those of an acute interstitial nephritis, such as that above mentioned as sometimes resulting from scarlet fever. This may perhaps be the case when the irritant is diffused from the pelvis in solution.

When the abscess-formation is one-sided, healing may take place. The kidney is then the seat of numerous cicatrices, a condition which Moxon has named the Cicatricial kidney.

Literature

Beck, Reynolds' Syst. of Med., v., 1879; Dickinson, 1. c.; Newman, 1. c.; Steven, Glas. Med. Jour., xxii., 1884; Moxon, Path, trans., xxiii., 1882.